Method of reproducing a relief image

ABSTRACT

This invention relates to a method of producing a copy image of a transparent relief image on at least one thermoplastic layer which comprises passing light from a substantially point source through a layer containing the relief image, and obtaining the copy image in a plane located at a distance other than zero behind the relief image.

a United States Patent ['19] Moraw etal.

[ METHOD OF REPRODUCING A RELIEF IMAGE [75] Inventors: Roland Moraw,Naurod; Gunther Schadlich, Wiesbaden, both of Germany [73] Assignee:Kalle Aktiengesellschaft,

Wiesbaden'Biebrich, Germany [22] Filed: Dec. 21, 1972 [21] Appl. No.:317,194

[30] Foreign Application Priority Data Dec. 24, 1971 -Germany 2164622 52us. Cl. 355/9 [51] Int. Cl. Gllb 3/00 [58] Field of Search 355/9, 91,132, 133

[56] References Cited UNITED STATES PATENTS 1,838,312 12/1931 Kanolt355/133 [4 1 May 7, 1974 3,653,888 4/1972 Lessman 355/9 3,207,051 9/1965Cooper 95/4.5 3,368,471 2/1968 Beato r 355/91 3,321,308 5/1967Walkup.....-. 355/9 Primary ExaminerJohn M. l-loran Attorney, Agent,orFirm-James E. Bryan, Esq.

[ ABSTRACT This invention relates to a method of producing a copy imageof a transparent relief image on at least one thermoplastic layer whichcomprises passing light from a substantially point source through alayer containing the relief image, and obtaining the copy image in aplane located at a distance other than zero behind the relief image.

8 Claims, 2 Drawing Figures I METHOD OF REPRODUCING A RELIEF IMAGE Theinvention relates to a method of reproducing, i.e., copying byprojection and/or duplicating, a transparent relief image on at leastone thermoplastic coating.

Relief images are obtained by various methods, usually photographicreproduction methods. Layers of photoresists can be so treated afterdeveloping that, depending upon the nature of the'coating, either, theexposed or the unexposed portions of the coating are removed. With theaid of dies, it is possible to impress imagesin deformable materials,particularly in thermoplastic films at high temperatures. Reliefduplicates also can be made from relief images by the impression methodwhereby the relief image is coated with a hardenable film-formingcomposition which is later removed. v

7 Relief images produced by electrophotographic methods may consist of acarrier, made of a dielectric, and optionally transparent material suchas 'a plastic substance or glass which may have a conductive coating oftin oxide, aluminum or the like, or a conductive material such asaluminum foil having a coating usually made of thermoplastic resintogether with photoconductive substances which may be present in theform of separate layers. The surface may 'be provided with anon-conducting coating which alters the light reflection. Thiselectrophotographic recording material is electrostatically chargedunder a corona discharge unit, exposed to produce the image andsoftened.

Under the effect of the latent charge pattern the surface of theplasticized resin deforms to provide a relief image. Depending upon thetest conditions and specifically upon the level of charge, differenttypesv of relief images are obtained. When the charge is relativelyhigh, the surface assumes an irregular structure in the charged areas sothat the image produced by lightscattering is obtained which can. beviewed or projected. This method of recording is known as the Frostprocess." If the recording material is not so heavily charged as for theFrost process, a continuous relief line is formed on the otherwisesmooth background which line marks the boundary where there is adiscontinuity in the magnitude of the charge as a result of exposure.This recording'process in which relief images consisting of continuousdeformation lines are obtained is known as P-hotoplastic Recording. Inthis specification, the term relief image will be understood to meanthis type of electrophotographic deformation image.

In recent years electrophotographic releif images have been the subjectof intensive development operations, and difficulties have beenencountered in projecting these images and particularly in-opticallyduplicating them. These relief images have been classified as phaseimages on account of the change in the thickness of coating. it has beennecessary to view them through phase microscopes. No suitableduplicating process has existed for relief images produced byelectrophotographic means. When impressions have been made, the reliefimage has been previously intensified by galvanic means. Casts usinghardenable coatings are timeconsuming to prepare. Copying by projectionhas been carried out by means of Schlieren optical systems.

The object of the invention is, therefore, to provide 1 a method ofreproducing relief images, and particularly relief images producedelectrophotographically, which avoids the aforementioned high costs andcomplications and which enables copies of relief images to be obtainedby projection and/or for the purpose of making duplicates.

The present invention provides a method for reproducing a transparentrelief image on at least one thermoplastic coating in which parallellight or divergent or convergent light from a point of substantiallypoint tion and good contrast when certain conditions regarding thedistance between the relief image to be reproduced and the plane of theimage are observed. Accordingto the invention, a distance is maintainedthat is large compared with the known duplicating processes used inconnection with photographic reproduction wherein the original and therecording material are in contact. It has been found that the distanceis roughly directly proportionalto the width of the relief line and canbe determinedwith the aid of the annexed graph (FIG. 1). The width (y)of the relief line and the distance (x) can be determined by theequation wherein x and y are in millimeters, m is between approximately0.02 and 0.15, and b is between approximately zero and -0.02.

Particularly good results can be obtained if m is between approximately0.03 and 0.07 and b is less than minus 0.01. These equations applyapproximately in the case of thicknesses of relief lineof 0.002 mm.

-'Thus, in the case of broad relief lines, the distance is greater thanwhen the relief lines are narrow. The preferred distance between therelief image and the plane of the image that enables copies havingmaximum contrast and sharpness to be obtained is within the rangeextending from approximately 0.1 to 5 mm.

Reproductions of relief images can be obtained by projection ontoscreens. However, it is preferred to make copies on copying materialsuch as diazo films or vesicular films in the plane of the copy image.Very considerable advantage results from the use of copying materialthat has a hard action and has a narrow exposure range in which theimage builds up. In the photographic industry, this latter property isgenerally specified quantitatively by the gradation.

Thus, legible duplicates are obtained by using diazo films havinggradation values of about 2. It has been found that contrast isconsiderably improved by the use of vesicular films which are thereforeparticularly suitable for the purpose of the present invention. Thesefilms have a softenable film-forming coating containing photosensitivesubstances which decompose when exposed to light-rays and form gaseousproducts, for example, aromatic diazo compounds, so that afterdeveloping, usually by thermal means, a high-contrast image formed bylight scattering is obtained. Gradation values of between 2.6 and 4.8are indicated for vesicular films having diazonium salts as thephotosensitive compoitems, in the production of light-scattering images,these values being dependent to some extent upon the optics'of thereproduction equipment.

According to the invention, by using the optimum distances found fromthe above-mentioned formulae, the relief images can be duplicated withparallel light while maintaining the same scale, as showndiagrammatically in the accompanying FIG. 2 wherein therelief-image 1,having. a striation width y, is shown as being reproduced in the plane 2at a distance of .t'. It is, however, also possible to obtain anenlarged image in the image planeby using divergent light as obtainedfrom 'a point orsubstantiallypoint source. It is also possible toproduce a reduced image by usingconvergent light as obtained from apoint source with a convergent lens. As in duplicating, all these imagescan be used for exposing a light-sensitive recording material, or theycan be captured for direct viewing on a screen. For the purposes ofprojection, the image in the image plane is projected onto the screen byway of an opticalsystem to the rear of the image plane. Various types ofreceiver's, for example light-sensitive recording elements, for exampletelevision camerasor photoelectric cells, are suitable as screens.

For the purpose of achieving uniform lighting of the objects to bereporoduced, use is generally made of areal lamps as employed induplicating or optical reproduction methods and containing severalcoils. of wire; use may also be made of one or more linearly extendinglamps, usually in the form of tubes, or of a sheet of ground glassinterposed between the object to be reproduced and the lamp. However,the use of such means results in a considerable reduction in contrastwhen reproducing'relief images. According to the invention, point lightsources are used for producing light having a controlled direction ofpropagation, such sources being, for example, gas-discharge lamps withshort arcs or incandescent lamps comprising a small coil, and the lightfrom these lamps may be reflected by way of a condensing unit. Thediameter of the light zonemust in each case be very much smaller thanthe distance between the relief image and the lamp. The use of parallellight represents a special case for reproducing the lighted zone withthe aid ofa condenser unit when the latter is located at adistance fromthe lighted zone that is precisely equal to the focal length. Lasers arealso suitable for the reproduction method of the invention, the laserbeam advantageously being broadened. When the light source is a laser,only its characteristic of an extremely small angle of divergence isemployed. Moreover, the phase coincidence occurring at the same time inthe laser beam leads to undesirable diffraction phenomena at the edgesof the image which, although not affecting resolution, do spoil theimpression given by the image.

Hitherto it has only been possible to use duplicating, in which theoriginal is in contact with the copying material, as a basis for theduplication of holograms laser light and the phase coincidence peculiarthereto being necessary for the duplication in order to enable thatportion of the beam passing through the hologram and that portiondiffracted thereon to interfere at the rear of the hologram. Apart fromthe fact that holograms are not-directly legible interference imageswhereas the relief images with which the'invention is concerned containinformation in the form of directly'legible symbols, in-phase light isrequired for the known method of duplicating holograms, whereas on theother hand phase coincidence is undesirable in the reproduction methodof the invention. It follows from this thatthe method of the inventionis not comparable with the'duplication of holograms.

As already stated, the plane in which a sharp copy'of the relief imageis obtained is located at a certain finite distance from the reliefimage and it is not necessary to interpose an additional opticalreproduction unit. Previously, it has been customary, when duplicatingon a non-contact basis, to provide an optical system behind the objectthat is to be optically reproduced.

In perfecting the method of reproducing relief images in accordance withthe invention, it has been found that the precise distance necessarybetween the relief image and the copying. material depends largely uponthe method used for producing the relief image. For example, for thepurpose of making sharp reproductions of relief images produced bystamping with a die having raised portions of rectangular cross-section,smaller distances are required that when producing sharp reproductionsof relief images produced by electrophotographic processes and probablyhaving a cup-shaped relief cross-section. A feature common to all reliefimages is that, for the purpose of reproduction, it is necessary tomaintain a certain distance which can vary up-.

wards or-downwards within certain limits, and although the informationbecomes increasingly more difficult to read, it still can beread untilcomprehensibility ceases completely when the distance is too great ortoo small. As previously stated, this is quantitatively represented inFIG. 1 in the case of relief images produced by electrophotographicmeans.

Conditions are more favorable for the reproduction of a relif originalconsisting only of letter type, for example, of a typewritten pagerecorded as a relief original to a different scale, or of computeroutput microfilm signals recorded in the form of electrophotographicrelief images.

The method of the invention will now be described in greater detail byreference to the following Examples. 1

EXAMPLE -I One gram of copper phthalocyanine, for example Microlith Blau4 GT, marketed by CIBA, Basle, Switzerland, 5 g of low-molecular weightpoly-2- methylstyrene, for example 276 V 9, marketed by Dow ChemicalCompany, U.S.A., and 10 g of polystyrene having an average molecularweight of appoximately 30,000, for example PS 3, marketed by Dow, weredis solved in 50 ml of CHCl The chloroform contained one spot ofsilicone oil per liter. Using this solution, a

50 p. thick polyester film was coated with a 2 u thick covering layer ofpolyvinyl chloride in a centrifuge, and was dried for 10 minutes at 21Cand then for 20 minutes at 50 C in a recirculated air drying cabinet.Charging was carried out in the dark on a grounded metal plate under a-8 KV needle corona. With the aid of a projection lamp (200 watt) animage reduced to one-fifteenth was produced over a period of 10 secondsfrom groups of striations of different sizes on the charged film throughan optical system (f 3.5 cm). The film was then developed by means of athermal radiator, the relief image thus being created. The radiatorwas asteel sheet located at a distance of 0.5 cm and having the dimensions20X 80 X 0.1 mm, to which 2.8 volts were applied for 1.5 seconds in thelongitudinal direction; the heating effect was approximately 0.5 KW. 3

The groups of lines on the relief image were measured off with the aidof a microscope. The relief image was then irradiated with parallellight from a point source high pressure mecury lamp (200 W) having aquartz lens (f= cm). A diazo film produced in the following manner waspositioned at predetermined distances behind the film carrying therelief image:

A cellulose acetate film was coated with the following solution and thendired: 2.6 g of citric acid, 6.0 g of thiourea, 1.4 g of2-hydroxy-3-naphthoic ac'id -(/3-hydroxyethyl)-arnide, 1.75 g of-3-hydroxy-'4- methylphenyl urea,- 1.2 ml of formic acid, 70 g of 4-diethylamino-benzenediazonium-tetrafluoroborate, 38 ml of water, and 48ml of isopropanol.

The diazo film was exposed for 60 seconds and developed with ammonia.The groups of lines recorded on the diazo film and observed in the formof a positive image in which the unexposed zones of the film weredarkened were detected with the aid of a microscope. The relationshipsbetween the necessary distance (x) and the thickness (y) of the relifstriation that were found are plotted in the annexed FIG. 1. Thedistance range which should be adhered to for producing legibleduplicateswas-located between the curves marked A and B. The valuesdetermined in accordance with thestated formula are:

r m b A 0.143 0.002 B 0.022 0.01 l

The preferred range of distances that enable duplicates of maximumcontrast and sharpness to be obtained was found to be approximatelymidway between the curves A and B and is indicated by hatching in FIG.

- 1. In accordance with the stated formula, the values for m and b wereas follows:

in b 0.06 0.001 0.039 0.003

Various lettering can be reproduced simultaneously in a legible mannerfor differing widths of striation, for which purpose reference should bemade to the graph for selecting a suitable distance.

The sharp reproduction of the relief image provided in the image planefor each width of striation can be projected by an optical system onto ascreen, a legible image being obtained.

EXAMPLE 2 The diazo film used in Example 1 was replaced by a vesicularfilm marketed by Kalvar, New Orleans, La., USA. The exposure time was 60seconds. Developing was effected by laying the vesicular film for 3seconds on a plate heated to about 100 C. This resulted in a negativelight-scattering image, i.e., the exposed portions of the film werecloudy. When the light-scattering image was projected, a high-contrastand very legible image was obtained. I

EXAMPLE 3 A zinc plate was coated with the following solution in acentrifuge and dried for 6 minutes at C:

100 ml of glycol monomethyl ether, 2.8 g of 1,2-naphthoquinone-2-diazide-5-sulfo-acid monoester of2,3,4-trihydroxybenzo-phenone (esterified in position 4) and 4.5 g ofnovolak having a melting range of between 108 and 1 18 C. This was thenexposed beneath an arc lamp through an original having groups of lines.After developing in an alkaline aqueous medium, ethching was carried outfor 20 seconds at 22 C using an iron chloride solution (40 Baume). Theflat etched image exhibited sharp edges under the microscope.

The zinc plate carrying the etched image was clamped, together with acolorless polyvinyl chloride film (100 1.1.), for 5 minutes in a vicehaving smooth jaws. The vice had been previously warmed with hot air.The impressed film was used in place of the electrophotographicallyproduced relief image of Example 1. Sharp images were obtained atdistances amounting to only about one-third of those used in Example 1.The exposure time for the diazo film when duplicating the relief imagein the polyvinyl chloride film was considerably shorter'than in Example1 and amounted to only approximately 5 seconds.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications;

What is claimed is:

1. A method of producing a copy image of a transparentelectrophotographic deformation image having relieflines on at least onethermoplastic layer, comprising passing light from a substantially pointsource through a layer containing said deformation image and onto saidthermoplastic layer while simultaneously maintaining a predetermineddistance x between said layer containing said deformation image and theplane of said thermoplastic layer, said distance x determined by theformula:

y m x b where:

y is the width of said relief lines in mm,

m is between about 0.02 and 0.15, x is said distance x in mm, and

b is between about 0 and minus 0.02, to obtain a copy image.

2. A method as claimed in claim 1 wherein a copying material is placedin the image plane.

3. A method as claimed in claim 2 wherein the copying material is onehaving a hard effect.

4. A method as claimed in clairri 3 wherein the copying material is avesicular film.

5. A method as claimed in claim 1 wherein the light is parallel light.

6. A method as claimed in claim 1 wherein the light is divergent light.

7. A methodas claimed in claim 1 wherein the light is convergent light.

2. A method as claimed in claim 1 wherein a copying material is placedin the image plane.
 3. A method as claimed in claim 2 wherein thecopying material is one having a hard effect.
 4. A method as claimed inclaim 3 wherein the copying material is a vesicular film.
 5. A method asclaimed in claim 1 wherein the light is parallel light.
 6. A method asclaimed in claim 1 wherein the light is divergent light.
 7. A method asclaimed in claim 1 wherein the light is convergent light.
 8. A method inaccordance with claim 1 wherein m is between about 0.03 and 0.07 and bis less than minus 0.01.